by Adam Shell, USA TODAY

For investors, the question is pretty much the same as the one posed by English punk rock band The Clash in 1981 in its popular tune Should I Stay or Should I Go.

Given that dilemma, we'll let investors make up their own minds. For a look at the bullish call, here are five reasons to buy now:

1. Bull has gas left in tank. History says there's more money to be made. The bull, which began in March 2009, is just entering its fourth and final stage, Laszlo Birinyi, founder and president of investment research firm Birinyi Associates, said in his 2013 preview. And the last phase, which he dubs the "exuberance" stage, historically has been a wildly profitable one for investors, with average gains of 38.7% in bulls since 1962. The first stage is "reluctance" (average gains of 49.4%), followed by "consolidation" (+6.4%), "acceptance" (+18.8%) and finally exuberance. "Our view," Birinyi wrote, "is that we are in the fourth leg of a bull market which will extend through most of 2013."

2. No signs of recession ahead. Economic contractions are often the cause of stocks heading lower. But incoming economic data are "not indicating that a recession is imminent," says James Stack, editor of InvesTech Research newsletter. He points to recent surveys that showed that both manufacturing and the services portion of the economy topped analysts' expectations in February and are at levels that suggest growth not contraction. An improving jobs market and a recovery in the housing market are also big economic pluses.

3. Cash stockpiles are ample. Capital is the fuel that powers bull markets. And right now there is no shortage of cash available that could eventually find its way into the stock market. "There's a lot of cash sloshing around the system," Birinyi notes. At the end of 2012, there was nearly $10 trillion parked in money market funds, bank savings accounts and certificates of deposit, according to Federal Reserve data. There's also another $1 trillion that has been funneled into bond funds in the past five years ended in 2012 by risk-averse investors, according to the Investment Company Institute, a fund company trade group. Add to that the roughly $1 trillion in cash sitting on balance sheets of non-financial companies in the Standard & Poor's 500-stock index, and you are talking about a lot of potential firepower.

4. Shift from bonds to stocks underway. Wall Street is dubbing it the "Great Rotation." In short, that catchy phrase describes an investor mind-set shift from playing it safe to taking risks again. And the asset allocation shift is already underway, according to Michael Hartnett, chief investment strategist at BofA Merrill Lynch. Want proof? In the seven weeks ended Feb. 20, net inflows to stock mutual funds totaled $54.2 billion. January marked the first month of positive cash flows for stock funds in a year, according to ICI data.

5. Market still priced right. Despite the Dow's 118% gain since the March 2009 low, stocks aren't pricey by historical standards. The broad market, as measured by the S&P 500, is trading at less than 15 times last year's earnings. That's not only lower than the average price-to-earnings ratio of 18.8 since 1998, but it is also lower than the peak P-Es in the past five bull markets, according to LPL Financial. In short, bull markets don't typically end with P-Es this low. At the last market peak, in 2007, the S&P 500 was trading at nearly 17 times earnings. Stocks were even more richly priced in 2000 when the P-E topped 28, LPL data show. "Bull markets end at higher stock market valuations," says Jeff Kleintop, chief market strategist at LPL.